Priority is claimed with respect to German Application No. 199 01 067.6-14 filed in Germany of Jan. 14, 1999, the disclosure of which is incorporated herein by reference.
1. Technical Field
The invention relates to an automated change-speed gearbox. More particularly, the invention relates to an apparatus for establishing a rotationally fixed and positive connection between a plurality of gears and a shaft.
2. Discussion
The prior art (DE 30 21 489 A1) has disclosed an automated change-speed gearbox of the same generic type in which two free gears are arranged coaxially with one another on an output-drive shaft. A sliding sleeve is arranged between the two free gears in such a way that it can be displaced axially both onto the first and onto the second free gear. This allows the respective free gear to be connected positively and in a rotationally fixed manner to the output-drive shaft. In addition, there is a tapered friction ring arranged in a rotationally fixed but axially displaceable manner on the output-drive shaft, this tapered friction ring thus allowing only a frictional connection to be established between one free gear and the output-drive shaft.
In this arrangement, the sliding sleeve is displaced by means of a first actuator, while the tapered friction ring is displaced by means of a second actuator.
One disadvantage of this change-speed gearbox is that the use of a separate actuator for the tapered friction ring is relatively expensive.
It is the object of the invention to provide a simple and low-cost automated change-speed gearbox which allows rapid engagement of a gear.
One advantage of the automated change-speed gearbox according to the invention is that a separate actuator for a frictional-torque transmission device is eliminated. The same actuator displaces a sliding sleeve both in one direction onto a first free gear to establish a positive connection and in the opposite direction onto a second free gear to brake or accelerate a first shaft against a second shaft by means of the frictional-torque transmission device. In this arrangement, both the sliding sleeve and the frictional-torque transmission device are advantageously supported against the same external teeth arranged in a rotationally fixed manner on the second shaft. This brings with it advantages in terms of costs and machining compared with separate support arrangements for the sliding sleeve, on the one hand, and the frictional-torque transmission device, on the other.
Another objective of the present invention is to provide an advantageous embodiment of the frictional-torque transmission device as a tapered friction ring. The operating force required for frictional engagement is reduced compared with that in other frictional-torque transmission devices, such as multi-plate clutches. The reason for this is the multiplication of the force due to the angle of taper included between the friction faces and the axis of the shaft.
An additional objective of the present invention is to provide a change speed gearbox having a particularly short axial length. By virtue of the fact that the profile of the second free gear has a I shape, the tapered friction ring can be arranged axially within a space enclosed by the second free gear.
A further objective of the present invention is to provide a simple and low-cost way of advantageously enabling a different material to be chosen for the tapered friction ring from that for the sliding sleeve.
A yet further objective of the present invention allows the use of thin tapered friction rings, which advantageously require relatively little axial installation space. However, these thin tapered friction rings are also more sensitive to jerky engagement of the frictional-torque transmission device than wide tapered friction rings. The frictional-torque transmission device is engaged less jerkily if the engagement force is increased progressively with time.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.